I see so many people asking this question or just way, WAY overpurchasing RAM so I thought I'd post this. There is a very simple & quick way of seeing if you actually are running low on RAM before buying 16GB (this is for Windows 7).

First, use your computer! Fire it up and launch all of the apps that you generally have going. Open a few browser tabs, get your email going, etc. Try to do an average session - don't open every app on your machine. In the example below, this is my laptop that's running Outlook, IE with several tabs, Chrome with several tabs, Notepad, Windows Explorer, a couple of chat apps, Dropbox and Snag-It.

Switch to the 'Performance' tab
Click the 'Resource Monitor...' button at the bottom of the window, and it will pop up a window that looks like this.

There are 5 different sections of memory usage on the bar graph, but only 3 of them are really important to you.

First one (in grey) is hardware reserved - this is RAM that hardware uses & there's nothing you can do about this, so not important. This amount will generally be pretty low.

Third one (in orange) is 'Modified'. Also not very important because this amount is generally low, but this is RAM that's in use by low priority tasks that can be quickly released for other use.

The green section is important - this is the total amount of physical RAM that your machine is currently using (ignoring the swap file). In the graphic below, the machine is using 3GB of RAM.

The next important section is dark blue (labeled 'Standby') - this is actually not labeled well, as this is your free or available RAM. This is memory that's available for use by whatever application needs it next. In this example, there's 3GB of RAM just waiting to be used.

Finally, the light blue section labeled 'Free' - this is also kind of misleading, as this is more like wasted RAM, not free RAM. The memory in this section is the amount that Windows is just ignoring because it has no use for it. It's not being used & it's not ready to be used by anything - it's just sitting there doing nothing.

So, if someone were to show me this display & ask if they need more RAM I'd say no way, as a matter of fact you already have too much installed. I'm only actually using 3GB with another 3GB on standby and 2GB doing nothing at all. As it's running now, having 4GB in the machine would be fine, and having 6GB would give me a safety buffer. It's got 8GB installed (see the line highlighted in yellow), so I'm wasting 2GB because Windows simply has no use for it.

What's annoying me is Chrome using so many processes, including for each plugin.

Why would this annoy you? There's no practical limit to the number of processes (for an every day user), so process isolation ala Chrome is a good way to design a browser. It lets you isolate each tab so that a failure in one doesn't bring down the whole application, and plug-ins can then be sandboxed to reduce the risk of a security exposure.

The memory overhead for an individual process isn't that much (they're not that much more heavy weight than threads) and the benefits are well worth any perceived downsides.

Alright I am reopening this thread and did as asked in removing the back and forth between a few members. Please keep it civil.

This is tech support and you guys have always been very good at policing yourselves and not making a mess that we have to clean up and I have always appreciated that and the good help that I have gotten from here. Play nicely please.

Basically, this preloads as much data and information as it can into RAM, for quick access and retrieval by the OS. It helps things such as speeding up application loading, OS booting, etc. So, while you may not utilize all the available RAM as is listed by the OP, your OS can still take advantage of additional RAM that you may have on your system. Remember, "unused RAM is wasted RAM".

Unfortunately, SuperFetch has been known to cause issues with some Vista systems, in that it causes the hard drive to be accessed continuously for extended periods of time, which ironically causes the system to slow down. This may also lead to additional wear on the hard drives, leading to eventual premature failure

There are some early cases of SuperFetch being an issue with HDD thrashing, and priority issues between SuperFetch and the rest of the I/O requirements of the OS. However, I believe that's largely been taken care of since then.

There are some early cases of SuperFetch being an issue with HDD thrashing, and priority issues between SuperFetch and the rest of the I/O requirements of the OS. However, I believe that's largely been taken care of since then.

It's an comment, without citation, on Wikipedia's page. Yes, if you search, you will see posts from 2006 and 2007 about it. Since that time, not only has Windows 7 come out (which was the basis of the creation of this thread), but that problem has ceased to be a mainstream issue (if it ever was one).

So no, that problem isn't an overbearing problem, nor does it detract from the main point of purchasing as much as you can, to provide for the SuperFetch performance improvements.

Two slots of DDR3? I'd recommend 8GB of RAM. Four? Go for 16GB of RAM.

Now, if you're stuck on DDR2, or even DDR, you have a bit of a tougher decision to make, since that's a bit more expensive (and don't even think about RDRAM!). DDR2 is about $40 for 4GB of RAM (twice as much as DDR3). I'd suggest 4GB of that as a good sweet spot with Windows Vista / 7.

If you still are stuck on DDR, well then I'd suggest upgrading your PC, rather than looking at adding more RAM to your current setup

It would be a waste of money.
You will NOT feel any difference from the faster ram. It's barely measurable, much less noticeable.
If you want to improve your computer's speed instead of buying a new one, then you should consider an SSD. The speed differences are remarkable and you'll feel like you got your money's worth, which wouldn't be the case, changing your ram to the higher speed modules.

It would be a waste of money.
You will NOT feel any difference from the faster ram. It's barely measurable, much less noticeable.
If you want to improve your computer's speed instead of buying a new one, then you should consider an SSD. The speed differences are remarkable and you'll feel like you got your money's worth, which wouldn't be the case, changing your ram to the higher speed modules.

4x DDR3 slots now supports 32GB which on HP P7-1235 supports out of the box it had 2x 4GB = 8GB. I've installed 4x 8GB with dual heatsink on both sides PC3-1280 240-pin CL11 for total of 32GB
Price $142 and free shipping or 2-day free shipping with Prime on Amazon. Can't beat that price.